1. Field of the Invention
The present invention relates to an operator cabin of a bulldozer, more particularly, an operator cabin of a bulldozer which is designed to provide improved visibility to its front working equipment, such as both end parts of a blade, and also the visibility at night by facilitating installation of work lamps.
2. Related Background Art
A commonly used operator cabin 51 is formed in a shape of truncated hexagonal pyramid, which is made up by a trapezoidal front part and a rectangular rear part as viewed from above as shown in FIG. 10, and has a front face 52 which is formed to be slantwise in its vertical direction with a fixed width. Accordingly, front side supporting pillars 53 are made to be straight. However, a bulldozer provided with an engine at the front side is disadvantageous in that, since the positions of the front side supporting pillars 53 of the operator cabin 51 are determined in view of the engine space, the visibility of right and left-side parts of the front equipment to the operator is obstructed by these front side supporting pillars 53. Therefore the operator has to incline his body to obtain visibility of the front working equipment while avoiding obstruction by the supporting pillars 53. The construction of the operator cabin 1, as illustrated in FIG. 11, is basically formed with a roof panel 72, side panels 73 and lower base frames. Lifting hooks 74 for lifting the operator cabin 71 and lowering it onto a bulldozer are generally welded to the roof panel 72.
For additionally installing a lamp on the roof of the operator cabin 71, lamp brackets 76 and 77, which are shown disassembled, are generally provided separately from the lifting hooks 74 and are installed on the operator cabin 71. However, a bracket retaining block 78 exclusively used for the lamp bracket is required to install the lamp brackets 76 and 77, and therefore the bracket retaining block 78 should be additionally welded to the roof panel 72. This welding work is extremely difficult for the following reasons. A skilled serviceman is required because the operator cabin is made of a thin sheet metal. Finish workmanship is important since the welded part can be seen from outside. Rust may appear on the welded parts. These reasons make it difficult to carry out field welding.
As described above, the operator cabin 71 is basically formed by the roof panel 72, side panels 73 and base frames. For assembling the roof panel 72 and side panels 73, a large-scale assembly jig has been used to ensure dimensional accuracy of the assembly. Lifting hooks for lifting the operator cabin 71 to install it on the bulldozer are welded to the roof panel 72. However, as shown in FIG. 12, the jig is formed as a box type frame 82 which surrounds the operator cabin 81 to hold the panels from the outside, and it is disadvantageous in that the welding service is extremely troublesome because the serviceman has to carry out welding work inside such complicated framework and the costs of such large-scale installation are expensive. In addition, as the operator cabin roof panel 84, to which lifting hooks 83 are welded as shown in FIGS. 13 and 14, is made of a thin sheet metal, there is a problem of defects of the welded parts and of distortion due to a load during a lifting operation with wire ropes 85.